1. Technical Field
Embodiments of the invention relate generally to a heating circuit, and more specifically, incorporating a thermally conductive substrate between the heating circuit and a target heating surface.
2. Prior Art
Piping and weldment systems that must operate at higher than ambient temperatures are typically heated using some sort of electrical resistance heater circuit. These circuits are held in close proximity to the target surfaces, and are typically insulated using some material wrapped around the outside, such as silicone rubber or fiberglass. In industrial applications, this insulation material serves several purposes including physical protection of the heater circuit from the environment, improving electrical and thermal efficiency by reducing thermal losses to the environment, increasing heater circuit life by reducing the chance of over-temperature and failure of the electrical resistance material, and improving personnel safety by reducing the touch temperature on the outside surface of the heated system.
Certain materials with low thermal K factors used as insulation will improve the above effects, but heat losses and thermal loading of the piping system and the components included in the system will effect the thermal uniformity from one point in the system to another, and unless the insulation is “perfect,” it alone is insufficient to provide the thermal uniformity across the system that is required in the semiconductor industry. The difference from high to low temperature across a system becomes worse as the operating temperature set point increases. Additionally, lack of thermal uniformity is compounded by the imperfection of the heater resistance element due to it's inherent hot and cold spots.
Electrical resistance heaters utilize a heat sink to be closely engaged with the heater surface for proper operation and longest service life. If the heater is allowed to operate in “open air,” it can overheat and fail much more quickly than if it is in intimate thermal contact with a heat sink. This accelerated failure mechanism becomes more prevalent as the operating temperature set point increases, especially as the thermal limits of the materials employed in the assembly are approached.
In high tech industries such as the semiconductor manufacturing sector, much finer uniformity is often required, with typical expectations on the order of plus or minus five degrees C. at a set point of up to 200 degrees C. Though it may be theoretically possible to achieve this level of uniformity using traditional heater construction methods, several iterations of the design may be required and the results lack manufacturing repeatability. Additionally, traditional heater construction often lead to very complex heater system design and finely controlled thermal balancing that can be affected by and thrown off by unpredictable changing environmental conditions.
Additionally, high tech industries are demanding that heated systems operate at higher and higher temperatures, often pushing the envelope for materials capability.
Thermal system designers require better methods for protecting the heaters, especially at higher operating temperature ranges, and for creating the desired high level of thermal uniformity.